1. Field of the Invention
The present invention relates to an apparatus and method for filling a hydrogen tank with hydrogen.
2. Description of the Related Art
Generally, a fuel cell, which generates electrical energy by an electrochemical reaction between hydrogen and oxygen, is supplied with hydrogen as a fuel from a hydrogen tank, which is located near the fuel cell and which stores hydrogen under a high pressure. When the amount of hydrogen that is stored in the hydrogen tank decreases, the hydrogen tank is connected to a high-pressure hydrogen storage tank, which stores hydrogen under a pressure higher than the hydrogen tank. Thus, the hydrogen tank is replenished with hydrogen supplied from the high-pressure hydrogen storage tank.
It is known in the art that when the hydrogen tank is filled with high-pressure hydrogen from the high-pressure hydrogen storage tank, the hydrogen inside the filled hydrogen tank generates heat. The temperature inside the hydrogen tank immediately after filling the hydrogen tank is higher than the ambient temperature, and is +70° C. or higher, for example. An increased pressure of hydrogen inside the hydrogen tank immediately after filling the hydrogen tank also develops at the high temperature, due to the rise in temperature. Thereafter, when the temperature inside the hydrogen tank drops, so as to be near to the atmospheric temperature, the pressure of hydrogen inside the hydrogen tank also drops to a level that is lower than the hydrogen pressure immediately after completion of filling the hydrogen tank. When the above temperature rise occurs, therefore, the filled hydrogen tank is likely to suffer a shortage of hydrogen.
Japanese Laid-Open Patent Publication No. 2005-69332 discloses, as a method of reducing a temperature rise in the hydrogen tank when thus-filling a hydrogen tank with hydrogen, a hydrogen supply station having a supply pipe for supplying hydrogen to a hydrogen tank on a vehicle from a plurality of high-pressure hydrogen storage tanks, which store the hydrogen under a plurality of different pressure stages. The hydrogen supply station also has a cooling means disposed within the supply pipe for cooling hydrogen as it flows through the supply pipe. The temperature inside the hydrogen tank is detected for enabling a feedback control. The hydrogen tank is filled with hydrogen, which is cooled by the cooling means, depending on the detected temperature inside the hydrogen tank.
According to the disclosed hydrogen supply station, the cooling means is disposed inside the hydrogen supply pipe, and the temperature inside the hydrogen tank is monitored and detected to enable feedback control, so as to cause the cooling means to initiate cooling of hydrogen dependent on the detected temperature. Consequently, a considerable time elapses after it is determined that the interior of the hydrogen tank needs to be cooled and until the hydrogen tank is filled sufficiently with cooled hydrogen. If the temperature inside the hydrogen tank is lowered excessively by the cooled hydrogen supplied thereto, then it is necessary to stop operation of the cooling means, and thereafter, to supply hydrogen at the atmospheric temperature to the hydrogen tank. It is quite time-consuming to fill the hydrogen tank with hydrogen at the atmospheric temperature. Therefore, the conventional hydrogen supply station is disadvantageous in that the temperature of the hydrogen used to fill the hydrogen tank is not highly responsive to temperature increases and decreases inside the hydrogen tank as it is being filled. Thus, the hydrogen tank cannot be filled with hydrogen while responding quickly to temperature changes inside the hydrogen tank.